Heterologous expression of TuCAX1a and TuCAX1b enhances Ca2+ and Zn2+ translocation in Arabidopsis.

KEY MESSAGE: TuCAX1a and TuCAX1b improved Ca2+ and Zn2+ translocation and TuCAX1b enhanced Ca2+, Zn2+, Mn2+ and Fe2+ content when exposed to Cd2+; Cd2+ translocation was inhibited under Ca2+ and Zn2+. Cation/H+ antiporters (CAXs) are involved in the translocation of Ca2+ and various metal ions in higher plants. In the present study, TuCAX1a and TuCAX1b, two cation/H+ antiporters, were isolated from the diploid wheat Triticum urartu, and their metal cation translocation functions investigated. TuCAX1a and TuCAX1b showed abundant tissue-specific expression in the internode and beard, respectively, and their expression levels were increased in shoots exposed to Cd2+, Zn2+ and Ca2+. Plant phenotype analysis showed that overexpression of TuCAX1a and TuCAX1b could improve the tolerance of Arabidopsis to exogenous Ca2+ and Zn2+. In the plant shoots and roots, the contents of Ca2+ and Zn2+ were higher than wild-type plants under Ca2+ and Zn2+ treatments, indicating that TuCAX1a and TuCAX1b can enhance Ca2+ and Zn2+ translocation. Ca2+, Zn2+, Mn2+ and Fe2+ contents showed higher accumulation in TuCAX1b-transgenic Arabidopsis shoots than in wild-type plants exposed to Cd2+, and the translocation of Cd2+ was inhibited under Ca2+ and Zn2+. Overall, the present study provides a novel genetic resource for improving the uptake of microelements and reducing accumulation of toxic heavy metals in wheat.